A preferred application for the present invention is in high-voltage, three-phase combined circuit switchers. Therefore, the background of the invention is described below in connection with such devices. However, it should be understood that, except where they are expressly so limited, the claims at the end of this specification are not intended to be limited to applications of the invention in association with such devices.
In general, a combined circuit switcher combines two circuit breaking devices in series: an interrupter (for example, a SF.sub.6 puffer interrupter), and a disconnect switch (for example, a lift arm with blade and jaw contacts). The interrupter is located inside an insulator which is also the lift arm of the disconnect switch. (i.e., a combined interrupter disconnect switch). Both breaking devices are driven by the same operating rod and connecting linkage.
To open the circuit, the operating rod must be pulled first at high speed to open the interrupter and then at slow speed to raise the switch arm and open the air disconnect switch. Similarly, to close the circuit, the operating rod must be pushed first at slow speed to lower the switch arm and close the disconnect switch and then at high speed to close the interrupter.
One type of combined circuit switcher for which the present invention is particularly suitable is a "V"-configuration combined circuit switcher (VCS). FIG. 1 shows a limited space application of a VCS designated generally as 100. Electrical energy flows from feeder 94, through VCS 100, to transformer 80, to an electrical load (not shown). VCS 100 is situated between transformer 80 and feeder 94 to break the circuit when desirable. Transformer bushing 82 sits atop transformer 80. Power line 84 is connected on one end to transformer bushing 82 and on the other end to a first terminal pad 116 on the VCS 100. Similarly, cable bushing 92 sits atop cable bushing support column 96. Power line 90 is connected on one end to cable bushing 92 and on the other end to a second terminal pad 104 on the VCS 100.
Another view of VCS 100 is provided in FIG. 2 which shows a typical VCS for a three phase power installation. A three phase power unit comprises three pole units 140A, 140B, and 140C: one pole unit for each power phase A, B, and C, respectively. The three pole units 140A-C are "gang-coupled" via interphase linkage 132. Interphase linkage 132 is also coupled to the operating rods 114A, 114B, and 114C of each of the pole units 140A-C, respectively. A single mechanism pullrod 300, also coupled to the interphase linkage 132, may be used to operate the breaking devices on all three pole units simultaneously.
As illustrated in FIG. 2, the VCS 100 is supported by a pair of support columns: left support column 128L and right support column 128R. An interphase linkage 132 is attached near one end 132L to the top of left support column 128L and near the other end 132R to the top of right support column 128R. A phase A pole unit 140A is located near the left end 132L of the interphase linkage 132, a phase B pole unit 140B is located near the center 132C of the interphase linkage 132, and a phase C pole unit 140C is located near the right end 132R of the interphase linkage 132.
A control cabinet 126 is located below the phase B pole unit 140B. The control cabinet 126 contains a combined operating mechanism (not shown in FIG. 2). The combined operating mechanism is the subject of the present invention and will be described in more detail below. A connecting support 130 is attached at its lower end 130L to control cabinet 126 and at its upper end 130U near the center of the interphase linkage 132C. The connecting support 130 contains the mechanism pullrod 300 that operates interphase linkage 132.
The components of a VCS pole unit 140 are illustrated in FIG. 1 which shows a side view of the VCS 100. The VCS pole unit 140 is substantially triangular in shape and comprises the following elements: station post insulator 102 which supports terminal pad 104 and jaw contact 106; support insulator 108 connected to lower bellcrank assembly 110 and to upper bellcrank assembly 112 and containing an operating rod 114; and combined interrupter disconnect switch arm 118 connected to upper bellcrank assembly 112 and comprising blade contact 120.
Disconnect switch arm 118 also contains a high speed interrupter. FIGS. 3A-3C, disclosed in U.S. Pat. No. 5,569,891 issued to Freeman et al., show a variety of cross sectional views of a typical high speed interrupter 10. The interrupter 10 provides two sets of contacts: arcing contacts 12 and 14, and main contacts 15 and 19. Arcing contacts 12 and main contacts 19 are movable to either close the circuit with respective contacts 14 and 15 or to open the circuit. FIG. 3A shows a cross section of the interrupter with its contacts closed; FIG. 3C shows a cross section of the interrupter with its contacts open.
The movable contacts 12 and 19 of high voltage circuit interrupters are subject to arcing or corona discharge when they are opened or closed, respectively. As shown in FIG. 3B, an arc 16 is formed between arcing contacts 12 and 14 as they are moved apart. Such arcing can cause the contacts to erode and perhaps to disintegrate over time. Therefore, a known practice (used in a "puffer interrupter" for example) is to fill a cavity 13 of the interrupter 10 with an inert, electrically insulating gas that quenches the arc 16. As shown in FIG. 3B, the gas is compressed by piston 17 and a jet or nozzle 18 is positioned so that, at the proper moment, a blast of the compressed gas is directed toward the location of the arc in order to extinguish it. Once an arc 16 has formed, it is extremely difficult to extinguish it until the arc current is substantially reduced. Once the arc 16 is extinguished as shown in FIG. 3C, the protected circuit is opened thereby preventing current flow.
As illustrated in FIG. 1, the circuit between feeder 94 and transformer 80 is closed when disconnect arm 118 is in the lowered position, with blade contact 120 engaging jaw contacts 106, and, as shown in FIG. 3A, movable contacts 12 and 19 engaging stationary contacts 14 and 15 within the interrupter.
To open the circuit, two sequential, linear movements of the mechanism pullrod 300 are required. First, the mechanism pullrod 300 must be moved in a first linear direction (downward, for example, as shown in FIG. 2) at high speed to open the interrupter 10. Then, the same mechanism pullrod 300 must be moved in the same linear direction (e.g., downward) at slow speed to raise the disconnect arm 118.
The interrupter 10 is opened by a high speed pull from the operating rod 114 acting on the upper bellcrank assembly 112. Upper bellcrank assembly 112, which comprises a system of levers (not shown), acts on arcing contacts 12,19 to open interrupter 10. Similarly, disconnect switch arm 118 is raised by a slow speed pull from the operating rod 114. A system of levers within lower bellcrank assembly translates the linear motion of the mechanism pullrod onto the operating rod.
Similarly, two sequential, linear movements of the mechanism pullrod 300 are required to close the circuit. First, the mechanism pullrod 300 must be moved in a second linear direction (e.g., upward as shown in FIG. 2) at slow speed to lower the disconnect arm 118. Next, the mechanism pullrod 300 must be moved in the same linear direction (e.g., upward) at high speed to close the interrupter 10.
Those skilled in the art will recognize that the rate at which the disconnect switch arm 118 is opened or closed is directly proportional to the rate at which the mechanism pullrod 300 is stroked. For a number of reasons it is undesirable to open or close the switch arm 118 too quickly. For instance, operating the switch arm 118 too quickly causes unnecessary wear on the blade contact 120 and jaw contacts 106, as well as on the other components of the switch arm 118. On the other hand, it is necessary to open and close the interrupter 10 quickly to control arcing. It should be understood that the rate at which the interrupter 10 is opened or closed is also directly proportional to the rate at which the mechanism pullrod 300 is stroked.
For example, the closing operation of a 145 kV VCS requires an initial slow speed stroke of the mechanism pullrod 300 to close the disconnect switch arm 118. This initial stroke is of about 176 mm linearly upward at about 38 mm/s. The interrupter 10 is then driven closed by a high speed stroke of the mechanism pullrod 300. The high speed stroke is of about 115 mm linearly upward at about 2-3 m/s. Similarly, the interrupter 10 is opened by an initial high speed stroke of the mechanism pullrod 300. This initial stroke is of about 115 mm linearly downward at about 4-6 m/s. Then the switch arm 118 is raised by a slow speed stroke of the mechanism pullrod 300. The slow speed stroke is of about 176 mm linearly downward at about 38 mm/s.
Those skilled in the art will recognize that the rate and distance parameters provided above will vary depending on the individual requirements of various combined circuit switchers. They are provided herein for purposes of clarity only and in no way limit the scope of the disclosed invention.
An operating mechanism which acts on a single mechanism pullrod to create a high speed linear motion of the mechanism pullrod in a first range of its motion and a slow speed linear motion of the same mechanism pullrod in a second range of its motion is desirable but, to the inventor's knowledge, is currently unavailable in the art.
Thus, there is a need in the art for an operating mechanism which opens a combined interrupter disconnect switch by acting on a mechanism pullrod to create a high speed linear motion of the mechanism pullrod, followed by a slow speed linear motion of the same mechanism pullrod. Further, there is a need in the art for an operating mechanism which closes a combined interrupter disconnect switch by acting on a single mechanism pullrod to create a slow speed linear motion of the mechanism pullrod followed by a high speed linear motion of the same mechanism pullrod.